Revert "[llvm-cxxfilt] Split and demangle stdin input on certain non-alphanumerics."

This reverts commit 5cd5f8f2563395f8767f94604eb4c4bea8dcbea0.
The test passes on linux, but fails on the windows build-bots.

This test failure seems to be a quoting issue between my test and
FileCheck on Windows. I'm reverting this patch until I can replicate
and fix in my Windows environment.

llvm-svn: 355021